For example, an electric vehicle braking device described in Patent Document 1 transmits a rotating force of an electric motor (power element) to a shaft member (spindle) via a reduction gear (gear unit), and allows a pressing member (brake piston) threadedly engaged with a shaft member to travel straight. Then, the pressing member presses a frictional member (brake pad) to generate a frictional force between the frictional member and a rotational member (brake disc), thereby generating a braking force on the wheel. In the electric braking device, the reduction gear is acoustically separated from the electric motor, which enables reduction of an electric-mechanic actuator in size and weight.
In an electric vehicle braking device described in Patent Document 2, a spherical surface member is interposed between a nut threadedly engaged with the shaft member and the pressing member. Contact surfaces of the spherical surface member and the pressing member are spherical surfaces, and grease is filled between the contact surfaces. A rotating force of an electric motor is transmitted to the shaft member via a reduction gear, and causes the spherical surface member and the pressing member to travel straight via the nut threadedly engaged with the shaft member. The pressing member presses the frictional member to generate a frictional force between the frictional member and a rotational member, thereby generating a braking force on a wheel. To release the braking force on the wheel, the electric motor is reversely rotated to put the spherical surface member into a free state, forming a gap between the contact surfaces of the spherical surface member and the pressing member.
The electric vehicle braking device described in Patent Document 2 transmits a rotating force of the electric motor to the shaft member via the reduction gear, and causes the spherical surface member and the pressing member to travel straight via the nut threadedly engaged with the shaft member. Then, the pressing member presses the frictional member to generate a frictional force between the frictional member and the rotational member, generating a braking force on the wheel. To release the braking force on the wheel, the electric motor is reversely rotated to put the spherical surface member into a free state and to form a gap between the contact surfaces of the spherical surface member and the pressing member. The electric braking device is provided with a load sensor for sensing the pressing force of the pressing member. The electric motor is controlled according to a detection signal of the load sensor.
Patent Document 3 describes a load sensor in which a sphere member is supported in a hole at the center of a deformable base, and four strain detection elements are formed around the sphere member. In the load sensor, when a load is applied to the sphere member in an inclined direction, the load is distributed by the sphere member and acts on the base. Thus, even if a load input direction is deviated, the load never acts on the base intensively, being reliably detected. The load sensor is used, for example, to detect a load applied to the frictional member in the brake-by-wire system.